1. Field of the Invention
The present invention relates to a voltage-controlled oscillator and particularly to a voltage-controlled oscillator in which an oscillating transistor and an amplifying transistor are connected in series in a DC manner and a resonance circuit is connected to the collector of oscillating transistor in view of preventing generation of irregular oscillation and enabling output level adjustment of the oscillation signal.
2. Description of the Related Art
There has been provided a voltage-controlled oscillator wherein an oscillating transistor and an amplifying transistor are connected in a DC manner and a resonance circuit is connected to the collector of the oscillating transistor. This voltage-controlled oscillator supplies an oscillation signal output from the emitter of an oscillating transistor to the base of an amplifying transistor, and outputs the oscillation signal from the collector of an amplifying transistor. Moreover, in this voltage-controlled oscillator, an irregular oscillation signal is sometimes generated in the frequency considerably lower than the frequency of oscillation signal with the influence of inductance connected in series to the collector of the oscillating transistor, and thereby generation of the irregular oscillation signal interferes with the intrinsic oscillation signal. Therefore, the irregular oscillation control circuit to control generation of irregular oscillation signal is, in more practical terms, an irregular oscillation control circuit connecting in series an inductor and a resistor connected to a series circuit between the collector of the oscillating transistor and the emitter of amplifying transistor.
Here, FIG. 4 is a circuit diagram illustrating an example of the structure of the well-known voltage controlled oscillator explained above.
As illustrated in FIG. 4, the typical voltage-controlled oscillator is composed of an oscillating active circuit portion 41, a resonance circuit portion 42, an oscillation signal output terminal 43, a power supply terminal 44, a frequency setting voltage supply terminal 45 and an irregular oscillation control circuit 46.
In this case, the oscillating active circuit portion 41 comprises a first transistor (oscillating transistor) 411, a second transistor (amplifying transistor) 412, a first coupling capacitor 413, a first feedback capacitor 414, a second feedback capacitor 415, an emitter resistor 416, a second coupling capacitor 417, a first base bias setting resistor 418, a second base bias setting resistor 419, a third base bias setting resistor 4110 , a first bypass capacitor 4111 , a second bypass capacitor 4112, a third coupling capacitor 4113, a load inductor 1414, a smoothing capacitor 4115, and also an irregular oscillation control circuit 46. The resonance circuit portion 42 comprises a resonance inductor 421, a varactor diode 422, a DC cut-off capacitor 423, a buffer inductor 424, and a smoothing capacitor 425. The resonance circuit portion 42 forms a resonance circuit mainly with the resonance inductor 421, and the varactor diode 422. The irregular oscillation control circuit 46 comprises an inductor 461, and a resistor 462. 
Each structural element 411 to 4115 forming the oscillating active circuit portion 41 and each structural element 421 to 425 forming the resonance circuit portion 42 are connected as illustrated in FIG. 4.
The well-known voltage controlled oscillator of the structure explained above operates as will be explained below.
When a frequency setting voltage is applied to a frequency setting voltage supply terminal 45, this frequency setting voltage is impressed to a cathode of the varactor diode 422 through the buffer inductor 424 to set a capacitance value of the varactor diode 422 corresponding to the frequency setting voltage. In this case, a resonance circuit consisting of the resonance inductor 421 and varactor diode 422 resonates at the frequency determined by the inductance value of resonance inductor 421 and capacitance value of varactor diode 422. During resonance of the resonance circuit, the oscillating active circuit portion 41 shows a negative resistance when the oscillation active circuit portion 41 is viewed from the resonance circuit portion 42. Therefore, a signal in the frequency identical to the resonance frequency is generated in the resonance circuit 42. When the frequency setting voltage to be supplied to the frequency setting voltage supply terminal 45 is changed, the capacitance value of the varactor diode 422 changes depending on such change and thereby the frequency of the frequency signal generated in the resonance circuit 42 also changes.
The oscillating active circuit portion 41 outputs, when the signal in the frequency identical to the resonance frequency is generated in the resonance circuit, such frequency signal from the emitter of the first transistor 411 as the oscillation signal and supplies this oscillation signal to the base of the second transistor 412 via the second coupling capacitor 417. The second transistor 412 amplifies the supplied oscillation signal under the grounded-emitter system and supplies the oscillation signal to the oscillation signal output terminal 43 from its collector via the third coupling capacitor 4113.
The oscillating active circuit portion 41 inserts an irregular oscillation control circuit 46 connecting in series the inductor 461 and the resistor 462 within the DC circuit between the collector of the first transistor 411 and the emitter of the second transistor 412. This irregular oscillation control circuit 46 impedes the irregular oscillation signal which is generated in the frequency considerably lower than the oscillation frequency signal supplied to the emitter of the second transistor 412 from the collector of first transistor 411 and also prevents, with connection of the irregular oscillation control circuit 46, that the irregular oscillation signal is supplied to the oscillation signal output terminal via the third coupling capacitor 4113 from the collector of the second transistor 412.
In this case, a resistor 462 used in the irregular oscillation control circuit 46 preferably has a resistance value as small as possible because it is connected to a DC circuit and generally it has the resistance value of 10 to 50 xcexa9.
The well-known voltage controlled oscillator described above has a merit that it can output the oscillation signal of the predetermined frequency band without generation of irregular oscillation; but it requires, on the other hand, insertion of the irregular oscillation control circuit 46 connecting in series the inductor 461 and resistor 462 within the oscillating active circuit portion 41 in order to control the irregular oscillation signal. Therefore, the number of parts increases and manufacturing cost rises as much in comparison with the voltage-controlled oscillator of this type where the irregular oscillation control circuit 46 is not inserted.
Moreover, the voltage-controlled oscillator of the related art includes an inductor 461 which is a large size electronic part requiring a large physical volume within the irregular oscillation control circuit 46 inserted to the oscillating active circuit portion 41 and therefore it is considerably difficult to reduce the size of total structure of the voltage-controlled oscillator.
Moreover, the voltage-controlled oscillator of the related art does not include an oscillation signal output level adjusting member. Accordingly, when it is requested to adjust the oscillation signal output level, the second transistor 412 must be replaced with one having a different amplification degree and the second coupling capacitor 417 must be replaced with one having a different capacitance value. Namely, many adjusting processes are required for output level adjustment of the oscillation signal.
The present invention has been proposed considering the technical background explained above and it is therefore an object of the present invention to provide a voltage-controlled oscillator which can reduce the number of parts, including large size electronic parts, and enables reduction in size of structure by eliminating the factor for generating irregular oscillation signal, and also can easily adjust the output level of oscillation signal.
In view of attaining the object explained above, the voltage-controlled oscillator of the present invention comprises an oscillating transistor which operates in a grounded-base system to output an oscillation signal, an amplifying transistor which operates in the grounded-emitter system to output an oscillation signal, and a resonance circuit connected to the collector of an oscillating transistor. The resonance circuit has a structure that a micro-strip line with an intermediate tap connected within a DC circuit between the collector of the oscillating transistor and the emitter of the amplifying transistor and a resonance capacitor connected between the collector of the oscillating transistor and the ground point are provided, and a coupling capacitor to transmit the oscillation signal is connected between the intermediate tap of the micro-strip line and the base of the amplifying transistor.
A mounting structure of the voltage-controlled oscillator of the structure explained above is composed of an upper layer on which individual structural elements insulated and provided opposed to each other including the oscillating transistor and amplifying transistor are mounted, an intermediate layer forming the micro-strip line and a lower layer forming the grounding layer, wherein a first conductive pattern and a second conductive pattern respectively forming the coupling capacitors to the upper layer and intermediate layer are provided opposed to each other, the first conductive pattern is connected to the intermediate tape of the micro-strip line and the second conductive pattern is connected to the base of the amplifying transistor.
According to the structure explained above, the resonance micro-strip line of the resonance circuit which can also be used in common as the power feeding line is inserted and connected, in place of the irregular oscillation control circuit, in a DC circuit between the collector of the oscillating transistor and the emitter of the amplifying transistor. Therefore, the resonance circuit may be structured with the resonance micro-strip line and resonance capacitor, and since an inductor which is the factor to generate irregular oscillation is not used, irregular oscillation can be prevented. In regard to the number of parts used in the voltage-controlled oscillator, since the structural elements of the irregular oscillation control circuit may be reduced by using at least the resonance micro-strip line and moreover the part to be reduced is a large size inductor element, the total structure of the voltage-controlled oscillator can be reduced in size in comparison with the total structure of the voltage-controlled oscillator of the prior art.
Moreover, according to the structure explained above, the output level of the oscillation signal can be adjusted simply, because the coupling capacitor for transmitting the oscillation signal is connected between the intermediate tap of the micro-strip line and the base of amplifying transistor; and the output level of the oscillation signal can be adjusted by changing the forming point and forming condition of the intermediate tap of the micro-strip line.